Friction engaged tilting roller bearing tape guidance

ABSTRACT

In one embodiment, a tape movement constraint comprises a tiltable tape roller bearing having a grooved surface adapted to contact and engage a surface of the tape as the roller barrel rotates. An actuator adapted to pivot the roller bearing surface controls the lateral position of a tape. In operation, in one embodiment, the roller barrel of the roller bearing is rotated by engaging a surface of the tape roller barrel with a longitudinally moving magnetic tape. At least a portion of any air bearing between the moving tape and the barrel surface is quenched using grooves formed in the barrel surface. The lateral position of the moving tape is sensed and the rotating roller barrel is tilted in response to the sensed lateral position of the moving tape to control the lateral position of the moving tape. Other embodiments are described and claimed.

RELATED APPLICATIONS

This application is a divisional application of parent application Ser.No. 12/028,663, filed Feb. 8, 2008, entitled “Friction Engaged TiltingRoller Bearing Tape Guidance, assigned to the assignee of the presentapplication, and incorporated by reference in its entirety.

FIELD

This description relates to tape drive systems for moving a tape, suchas a recording tape for storing information, longitudinally across ahead where the tape is subject to lateral movement.

BACKGROUND

Typically, tape drive systems provide tape guides for controlling thelateral movement of the tape as the tape is moved along a tape path in alongitudinal direction across a tape head. The tape may have a pluralityof data tracks extending in the longitudinal direction, and the tapedrive system may provide a track following servo system for moving thetape head in a lateral direction for following lateral movement of thelongitudinal tracks as the tape is moved in the longitudinal direction.The track following servo system may employ servo tracks on the tapewhich are parallel to the data tracks, and employ servo read heads toread the servo tracks to detect position error and thereby position thetape head at the data tracks and follow the data tracks. This allows thedata tracks to be placed closely together and increase the number ofdata tracks.

The tape is typically contained in a cartridge of one or two reels, andthe tape is moved between a supply reel and a take up reel. The reelstypically have runout causing the tape to move laterally as the tape ismoved longitudinally. Tape guides can to an extent limit at least theamplitude of the lateral movement of the tape with the goal of limitingthe lateral movement so that it does not exceed the lateral movementcapability of the track following servo system.

In functions other than tape guiding, such as a tension roller (U.S.Pat. No. 4,310,863), an inertia roller (U.S. Pat. No. 4,633,347), or atape timer roller (U.S. Pat. No. 3,037,290), where only longitudinalmotion of the tape is concerned, high friction rollers that are in thetape path and displaced a considerable distance from the tape head, areintended to prevent or reduce tape slippage longitudinally with respectto the roller.

Typical tape guides may comprise stationary buttons or edges, or flangesat the side of tape guide rollers, positioned against the edges of thetape to control the amplitude of the lateral movement of the tape. Inorder to increase the total capacity of a tape, the tape is increasinglymade thinner to allow more wraps of tape to fit on a given tape reel. Asa result, the tape can be relatively weak in the lateral direction, andcan, in some instances, be relatively easily damaged at the edge fromthe tape guide. Thus, the tape guides are typically positioned at abearing where the tape assumes a cylindrical shape, thus increasing theability of the tape edge to support a load. The tape roller bearing isgenerally rotatable about a central axis parallel to the cylindricalperipheral surface, allowing the tape freedom of movement in thelongitudinal direction.

The bearing is also typically designed to have low friction. Thisarrangement can minimize the potential to distort the edge of the tapeas the guides push against the edges of the tape to move the tape to thecenter of the bearing to reduce the amplitude of lateral displacement ofthe tape. One example is illustrated in U.S. Pat. No. 5,447,279, whichemploys an air bearing to reduce the friction of the bearing forstationary tape guides. One type of bearing in which the tape engagementsurface remains stationary may also be referred to as a fixed pin orpost. Other bearings such as roller bearings may have rotating tapeengagement surfaces which reduce the longitudinal friction of thebearing while the flanges of the roller bearings push against the edgesof the tape. One example of a roller bearing or fixed pin with flangesarranged to have low friction is U.S. Pat. No. 4,427,166. Fixed surfacesmay also be arranged to have low friction. One example is described inU.S. Pat. No. 4,466,582, where a synthetic resin or metal coated tapeguide bearing has a reduced contact area for the tape to lower thefriction between the guide surface and the running tape and allow theflanges to stabilize the tape.

However, when wound on a reel, tape is typically subjected to stackshifts or stagger wraps, in which one wrap of the tape is substantiallyoffset with respect to an adjacent wrap. Thus, as the tape is unwoundfrom the reel, there can be a rapid lateral transient shift of the tape.Other common sources of rapid lateral transient shifts include 1) abuckled tape edge in which the tape crawls against a tape guide flangeand suddenly shifts laterally back down onto the bearing, 2) a damagededge of the tape which causes the tape to jump laterally when contactinga tape guide, and 3) when the take up reel or supply reel runout is sosignificant that the reel flange hits the edge of the tape.

Because of the low friction of the bearing and the low mass of the tape,rapid lateral transient shift of the tape at any point of the tape pathmay not be slowed by the typical tape guide and thus may be transmittedalong the tape path to the tape head.

A tape head track following servo system may comprise a single actuator,or a compound, multiple element actuator. The transient response of thetape head track following servo system typically comprises a highbandwidth for a very limited lateral movement, called “fine” trackfollowing, to permit the tape head to follow small displacements of thetape. Larger movement of the tape head is typically conducted as“coarse” track following, which is also employed to shift the tape headfrom one set of tracks to another set, and is typically conducted at aslow rate. The occurrence of a lateral transient shift, however, can beso rapid that neither the fine track follower nor the coarse trackfollower is able to respond, with the result that the tracking errorbecomes so large that writing may be stopped to prevent overwriting anadjacent track and to insure that the tracking error on read back is notso large as to cause a readback error.

One approach has been to make the tape guide edges or flanges closertogether to maintain a pressure on both edges of the tape. However, thistends to stress and damage the edges of the tape, reducing itsdurability. An attempt at reducing the stress comprises spring loadedtape guides, such as the above-mentioned '279 patent. However, althoughthe amplitude of the tape shift may be reduced somewhat by thisapproach, the speed of the shift is typically not reduced, and a trackfollowing servo error may still occur, reducing the performance of thetape drive.

U.S. Pat. No. 6,754,033 describes a tape roller bearing having acylindrical peripheral surface comprising a grooved frictional surfacefor contacting and engaging the surface of the tape, allowing the tapeto move freely with the tape roller bearing cylindrical peripheralsurface in a direction perpendicular to the central axis, andconstraining movement of the tape in the lateral direction. Thefrictional surface limits slip in the lateral direction, therebyreducing the rate of the lateral transient movement of the tape to allowthe track following servo system to follow the reduced rate lateraltransient movement of the longitudinal tracks.

Thus, the tape is contacted and engaged at its surface rather than at anedge, constraining the tape in the lateral direction, providingsubstantial lateral drag to the tape, such that the tape is able to movelaterally at a slower rate as the tape roller bearing rotates, which cansubstantially reduce the rate of the lateral transient movement. Thegrooved tape engagement surface substantially quenches any potential airbearing that could form between the surface of the tape and the surfaceof the roller bearing, e.g., due to the air drawn along by the tape asit is moved rapidly. As a result, an air bearing beginning to form isgenerally collapsed to ensure that the roller bearing frictionallycontacts and engages the surface of the tape. A flat cylindrical surfacemay also be provided at the edges of the tape to fully support the tapeedges.

Another approach has been to provide rollers having a crowned tapeengagement surface which exerts a lateral force on the tape which tendsto restore the tape to a central position. However, the effectiveness ofthis approach can be limited due to various factors such as the Young'sModulus exhibited by the tape and the degree of strain permitted to beexerted on the tape.

Yet another approach utilizes a post having a concave tape engagementsurface rather than a crowned tape engagement surface. Here too, thecurvature can provide some restoring force to center the tape. However,like the crowned tape engagement surface, the concave curvature islimited by the allowable tension gradient in the tape. Typically, thetension gradient is maximum when the tape is at nominal tension and theedges are “baggy” or at zero tension.

It has also been proposed to use sensors to detect the lateral positionof the tape edge as it passes the bearing and to tilt the bearing in anactive closed control loop to control the lateral position of the tape.It is recognized that tilting the bearing can introduce a gradient oftension between the top and bottom edges of tape which can be used toactively steer the tape riding on an air bearing formed between the tapeand the physical bearing surface. However, the air bearing may beinadvertently quenched such as when the tape stops or momentary stictionoccurs between the tape and the physical bearing surface. As aconsequence, a momentary loss of control of the tape may be producedwhich may have severe consequences causing damage to the tape.

SUMMARY

A tape movement constraint is provided for a tape drive system. In oneembodiment, the tape movement constraint rotates a tape roller barrel ofa roller bearing by engaging a surface of the tape roller barrel with alongitudinally moving magnetic tape, quenching at least a portion of anyair bearing between the moving tape and the barrel surface using groovesformed in the barrel surface, sensing the lateral position of the movingtape, and tilting the rotating roller barrel in response to the sensedlateral position of the moving tape to control the lateral position ofthe moving tape

In the illustrated embodiment, the tape roller barrel is tilted bydriving an electric current which is conducted by a coil held by a coilholder at least partially disposed within the roller barrel, to generatea magnetic field which interacts with a magnetic field of a permanentmagnet to move the coil and its coil holder. A hinge, at least a portionof which is disposed in the coil holder, allows the coil holder to pivotrelative to a first support frame.

In the illustrated embodiment, the hinge provides a pivot axis alignedwith a center position of the roller barrel surface in the lateraldirection. Also, the hinge is a living hinge having a flexure membercoupled by a first hinge member to the coil holder, and a second hingemember coupled to the first support frame.

In the illustrated embodiment, the tiltable tape roller bearing of theconstraint system is positioned along the tape path closely adjacent thetape head, has a cylindrical peripheral surface parallel to the lateraldirection of the tape and extending a length greater than the width ofthe tape, for contacting a surface of the tape. The tape roller bearingis rotatable about a central axis parallel to the cylindrical peripheralsurface, allowing the tape freedom of movement in the longitudinaldirection.

The tiltable cylindrical peripheral surface comprises a frictionalsurface for contacting and engaging the surface of the tape, allowingthe tape to move freely with the tape roller bearing cylindricalperipheral surface in a direction perpendicular to the central axis, andconstraining movement of the tape in the lateral direction. Thefrictional surface limits slip in the lateral direction, therebyreducing the rate of the lateral transient movement of the tape to allowthe track following servo system to follow the reduced rate lateraltransient movement of the longitudinal tracks.

Thus, the tape is contacted and engaged at its surface rather than at anedge, constraining the tape in the lateral direction, providingsubstantial lateral drag to the tape, such that the tape is able to movelaterally at a slower rate as the tape roller bearing rotates,substantially reducing the rate of the lateral transient movement. Inone embodiment, any potential air bearing that could form between thesurface of the tape and the surface of the roller bearing, e.g., due tothe air drawn along by the tape as it is moved rapidly, is collapsed toinsure that the roller bearing frictionally contacts and engages thesurface of the tape.

The tape drive system moves the tape along a tape path in a longitudinaldirection across a tape head, the tape having tracks extending in thelongitudinal direction, the tape head having a track following servosystem for moving the head in a lateral direction for following lateralmovement of the longitudinal tracks, where the tape is subject tolateral transient movement.

Other embodiments are described and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the present description, reference shouldbe made to the following detailed description taken in conjunction withthe accompanying drawings.

FIG. 1 is a partially cut away perspective view of a tape drive inaccordance with one embodiment of the present description;

FIG. 2 is an isometric view, illustrating one embodiment of a tiltableroller bearing in accordance with the present description, which may beemployed in the tape drive of FIG. 1;

FIG. 3 is a side schematic diagram of one embodiment of a constraintsystem in accordance with the present description, which may be employedin the tape drive of FIG. 1;

FIG. 3 a is a top, schematic view of one embodiment of the interactionof permanent magnets and a coil in an actuator of a tiltable rollerbearing in accordance with the present description;

FIG. 4 is an exploded assembly drawing, illustrating one embodiment of atiltable roller bearing in accordance with the present description,which may be employed in the tape drive of FIG. 1;

FIGS. 5 a and 5 b are schematic diagrams illustrating a non-tiltposition and a tilt position, respectively, of a flexural pivot used inone embodiment of a tiltable roller bearing in accordance with thepresent description, which may be employed in the tape drive of FIG. 1;

FIG. 6 is an enlarged isometric view of hinge members of a flexuralpivot used in one embodiment of a tiltable roller bearing in accordancewith the present description, which may be employed in the tape drive ofFIG. 1;

FIG. 7 is a flowchart depicting one example of operations of a tapeconstraint in accordance with the present description;

FIGS. 8 a and 8 b depict one example of dynamics of operation of a tapeconstraint in accordance with the present description;

FIGS. 9 a and 9 b are enlarged views of alternative embodiments of theroller bearing barrel of FIG. 2;

FIGS. 10-13 are enlarged views of alternative embodiments of the rollerbearing barrel of FIG. 2; and

FIGS. 14 a and 14 b are diagrammatic representations of alternativeembodiments of peripheral surfaces of the roller bearing barrel of FIG.2 in accordance with the present description.

DETAILED DESCRIPTION

In the following description with reference to the Figures, like numbersrepresent the same or similar elements. While this description isprovided in terms of the best mode, it will be appreciated by thoseskilled in the art that variations may be accomplished in view of theseteachings without deviating from the spirit or scope of the presentdescription.

Referring to FIG. 1, a tape drive 10, such as a magnetic tape drive, inaccordance with one aspect of the present description, is illustrated. Amagnetic tape 11 is moved along a tape path from a supply reel 12 in amagnetic cartridge 13 to a take up reel 14, the reels comprising drivereels of a drive system operated by drive motors. The magnetic tape ismoved along the tape path in a longitudinal direction across a tape head15. The tape head is supported by an actuator 17 of a servo system,which, for example, may comprise a compound actuator. The tape head 15,for example, a magnetic tape head, may comprise a plurality of read andwrite elements and a plurality of servo read elements. The tape maycomprise a plurality of servo tracks or bands 18 which are recorded onthe tape in the longitudinal direction on the tape and are parallel tothe data tracks. The servo read elements are part of a track followingservo system for moving the tape head 15 in a lateral direction forfollowing lateral movement of the longitudinal tracks as the tape 11 ismoved in the longitudinal direction, and thereby position the tape headat the data tracks and follow the data tracks.

The compound actuator may comprise a coarse actuator, such as a steppermotor, and a fine actuator, such as a voice coil, mounted on the coarseactuator. The fine actuator in this embodiment has a high bandwidth fora very limited lateral movement, called “fine” track following, forallowing the tape head to accurately follow small displacements of thetape. Larger movement of the tape head is in this embodiment conductedby the coarse actuator for centering the actuator at the averageposition of the fine actuator during track following, and is alsoemployed to shift the tape head from one set of tracks to another set,and is conducted at a slow rate. An example of a compound actuator isdescribed in coassigned U.S. Pat. No. 5,793,573. It is appreciated thatmany differing types of actuators may be employed in embodiments of thepresent description, depending upon the particular application.

The tape drive 10 additionally comprises a controller 20 which providesthe electronics modules and processor to implement a servo system tooperate the compound actuator. In addition, the controller 20 providesthe electronics modules and processor portion of the tape movementconstraint described below.

The magnetic tape 11 of the present example may be provided in a tapecartridge or cassette 13 having a supply reel 12 or having both thesupply and take up reels. The servo tracks or bands 18 may comprise anyof several types of longitudinal servo patterns as is known to those ofskill in the art. For example, a timing based servo pattern is describedin coassigned U.S. Pat. No. 5,689,384, and comprises magnetictransitions recorded at more than one azimuthal orientation across thewidth of the servo track. In one example, five longitudinal timing basedservo tracks are prerecorded on the magnetic tape for track following atthese positions. The pattern of magnetic transitions recorded in theservo tracks is a repeated set of frames, each of which are of differentazimuthal orientations. Thus, the tape head 15 may comprises at leasttwo narrow servo read elements allowing two servo tracks to be sensedsimultaneously, and the outputs used redundantly to reduce error rates.

In this example, the magnetic tape 11 may also be provided with suitableguard bands at the edges of the tape, and four data track regionsbetween the servo tracks. A plurality of read and write elements may beprovided at the tape head 15 for reading and/or writing data on the tape11. When the servo elements are properly positioned at the specificservo tracks, the read and write elements are properly positioned totransfer data with respect to the corresponding data track locations ofthe tape 11.

The data tracks are typically narrow and closely spaced, and the tape 11is typically very thin with little lateral stiffness at the edge. Tapeedge guides may be provided which push against the edge of the tape toprevent excessive lateral movement of the tape, for example, from runoutof the supply reel 12 or the take up reel 14, at least from thestandpoint of the amplitude of the movement of the tape. However, whenwound on a reel, tape is typically subjected to rapid lateral transientshifting, for example, from stack shifts or stagger wraps, in which onewrap of the tape is substantially offset with respect to an adjacentwrap. Other common sources of rapid lateral transient shifts include 1)a buckled tape edge in which the tape crawls against a tape guide flangeand suddenly shifts laterally back down onto the bearing, 2) a damagededge of the tape which causes the tape to jump laterally when contactinga tape guide, and 3) when the take up reel or supply reel runout is sosignificant that the reel flange hits the edge of the tape.

In the tape drive 10 of FIG. 1, a tape movement constraint in accordancewith one embodiment of the present description, comprises at least onetape roller bearing 60, 61 for positioning the tape 11 along the tapepath closely adjacent the tape head 15. Each tape roller bearing 60, 61has a generally cylindrical peripheral surface 200 (FIG. 2) parallel tothe lateral direction of the tape 11 (FIG. 1) and extending a height orlength L (FIG. 3) greater than the width of the tape 11, for contactinga surface of the tape 11. In the illustrated embodiment, the height L ofthe barrel is chosen to be 16 mm to comfortably handle possible lateralexcursions of a half-inch (12.7 mm) wide tape 11. It is appreciated thatother dimensions may be selected depending upon the particularapplication. Each tape roller bearing 60, 61 is rotatable about acentral axis 210, parallel to the cylindrical peripheral tape engagementsurface 200, allowing the tape freedom of movement in the longitudinaldirection and also countering stiction.

In accordance with one aspect of the present description, the tapeengagement surface 200 of each tape roller bearing 60, 61 is tiltable tocontrol the lateral position of the moving tape, and is also textured,that is, grooved, to enhance lateral friction to a degree between thetape and the engagement surface 200. In the illustrated embodiment, thetape engagement surface 200 of each tape roller bearing 60, 61 istiltable about an axis, such as the axis 214, for example, which, inthis embodiment, is generally orthogonal to the axis 210 of rotation ofthe tape roller bearing 60, 61. As explained in greater detail below,the tilt of the roller bearing 60, 61 may be controlled to counteractlateral movements of the tape. As a consequence, the rate of the lateraltransient movement of the tape may be reduced so that the trackfollowing system may continue to track follow the longitudinal tracks ofthe tape. It is appreciated that in other applications, features otherthan reduction of lateral transient movement may be achieved, dependingupon the particular application.

In the illustrated embodiment, the tape movement constraint comprises atleast one tape roller bearing, and preferably comprises two tape rollerbearings 60 and 61, positioned along the tape path at either side of andclosely adjacent the tape head 15. Alternatively, tape roller bearings60 and 61 may be located within a removable cartridge, for example,replacing the stationary bearings in an IBM 3570 tape cartridge, forexample. When the cartridge is placed in the drive, the tape rollerbearings 60 and 61 are positioned along the tape path, and closelyadjacent the tape head 15. Elements 112 and 113 may compriseconventional tape guides for reducing the amplitudes of the lateraltransient movement, or may comprise additional tape movement constraintroller bearings. It is appreciated that the tape roller bearings of theconstraint may be positioned elsewhere with respect to the tape head,depending upon the particular application.

FIG. 3 is a schematic diagram of one example of a tape movementconstraint 300 for a tape drive system for a tape. FIG. 4 is an explodedassembly view of one example of a physical embodiment of the tape rollerbearing 60 of FIG. 2 depicted in schematic form in FIG. 3. In thisexample, the tape movement constraint 300 includes the tape rollerbearing 60 having a base 302 which has a first support frame 304. Asbest seen in FIG. 2, a cylindrically shaped member 305 at the bottom ofthe base 302 may be used to locate and fasten the tilting roller bearing60 to the drive 10. A second support frame 306 is pivotally coupled at apivot 308 to the first support frame. A tape roller barrel 310 of thetape roller bearing 60 is rotatably supported by the second supportframe 306. The roller barrel 310 is positioned along a tape path, and inthis example, the surface 200 of the roller barrel 310 defines aplurality of grooves 312, so that the surface 200 is adapted to contactand engage the surface of the tape 11 as the roller barrel 310 rotates.

An actuator 320 is coupled to the second support frame 306 and isadapted to pivot the second support frame and the roller barrel 310 atthe pivot 308 relative to the first support frame 304 when the actuator320 is actuated. In the illustrated embodiment, the actuator 320 is avoice coil actuator. It is appreciated that other types of actuators maybe used, depending upon the particular application.

The tape movement constraint 300 further includes a tape position sensor324 positioned to detect the lateral position of the tape 11. Thecontroller 20, responsive to the tape position sensor 324 is adapted tocontrol the actuator 320 to tilt the roller barrel 310 on the pivot axis214 to control the lateral position of the tape 11 in response to thetape position sensor 324.

In the illustrated embodiment, the voice coil actuator 320 includes acoil 330 which is adapted to conduct an electric current to generate amagnetic field. The actuator 320 further comprises at least onepermanent magnet 340 disposed in the base 302. In the illustratedembodiment of FIG. 4, the base 302 includes a pair of magnets 340disposed on either side of the coil 330 and housed within a magneticreturn path 342 of the base 302. As best shown in the side and topschematic views of FIGS. 3, 3 a, the magnets 340 are positioned so thattheir magnetic fields interact with the magnetic field generated by thecoil 330 to cause the coil 330 to pivot on pivot 308 with respect to themagnets 340 of the base 302. Thus, current through the coil 330 producesa force normal to the wires of the coil 330 and the magnetic fields ofthe magnets 340. The magnetic fields of the magnets 340 are about normalto the plane of FIG. 3. Consequently, the force applied to the coil 330is in the left/right (L/R) direction (depending upon the currentdirection) in FIGS. 3, 3 a. This force causes tilting of the rollerbearing 60 about the flexural pivot 308.

The second support frame 306 includes coil holder 350 which is adaptedto hold the coil 330. As best shown in FIG. 4, the coil holder 350 isgenerally cylindrical in shape and supports a pair of roller bearingtracks 352 positioned around the coil holder 350. The roller bearingtracks 352 in turn engage the internal surface of the roller barrel 310,wherein the roller barrel 310 is adapted to rotate on the roller bearingtracks 352 around the coil holder 350 of the second support frame 306.In the illustrated embodiment, the roller bearing tracks 352 may includeball bearings, an air bearing, or other suitable bearings.

In the illustrated embodiment, the coil holder 350 is rigidly attachedto the coil 330, so that motion of the coil 330 is directly transmittedto the coil holder 350, bearing tracks 352, and the barrel 310. Asdescribed in greater detail below, the motion of the coil holder 350 isconstrained by the flexural pivot at the pivot point 308.

In the illustrated embodiment, the roller bearing tracks 352 are angularcontact or deep groove ball bearings, preloaded against each other topermit smooth rolling motion of the barrel 310. In that there is littleor no relative motion of the tape with respect to the roller in thisembodiment, the tape movement constraint 300 can facilitate control ofhigh frequency excitation of lateral motion of the tape 11. Accordingly,such control may be facilitated if the bearing tracks 352 haverelatively little radial and axial runout. However, it is appreciatedthat other types of bearings may be used, depending upon the particularapplication.

FIG. 5 a is a schematic diagram of one example of the pivot 308. In thisembodiment, the pivot 308 comprises a hinge 500 disposed in the coilholder 350 wherein the coil holder 350 of the second support frame 306is pivotally coupled to the first support frame 304 by the hinge 500. Inthis example, the hinge 500 is a living hinge which includes first andsecond hinge members 510, 520 and a flexure member 530 flexibly couplingthe first hinge member 510 to the second hinge member 512. FIG. 5 bdepicts the flexture member folded so that the second support frame 306is pivoted at pivot 308 relative to the first support frame 304.

FIGS. 4 and 6 show one example of a physical embodiment of the hinge 500with the flexture member 530 omitted for clarity. The first hinge member510 is coupled by a plate 610 to the coil holder 350, and the secondhinge member 520 extends from a member 620 of the first support frame304. The member 620 is, in this embodiment disposed within the coilholder 350 and is coupled to a base cover member 630 of the firstsupport frame 304.

In the illustrated embodiment, the plate 610 of the second support frame306 is rigidly attached to the coil holder 350 so that the first hingemember 510 is rigidly coupled to the coil holder 350. Conversely, thesecond hinge member 520 is rigidly connected by the member 620 (FIG. 6)of the first support frame 304 (FIG. 4) to the base cover member 630,which is rigidly attached to the magnetic return path 342 of the base302.

The living hinge 500 including the flexture member 530 provides aflexural pivot, having a predetermined stiffness which is low enough toprovide a relatively low frequency resonance. For example, the livinghinge may provide a low frequency resonance near 10 Hz. Conversely, theliving hinge 500 may be sufficiently stiff to provide a restoring forcelarge enough to center the roller bearing 60 without forces external tothe bearing.

In the illustrated embodiment, to offset lateral forces which may beproduced by the tape 11 due to tension, the pivot 308 is placed at themidpoint of the barrel 310 of the roller bearing 60 as shown in FIG. 3Thus, the roller barrel surface 200 has a center position 360 in thelateral direction and the pivot axis 214 defined by the pivot 308 isaligned with the center position 360. In another aspect of the presentdescription, the center of mass of the moving part of the actuator 320may be positioned close to the pivot 308 to alleviate effects due toexternal vibrations. It is appreciated that the pivot 308 and actuator320 may be positioned in other positions, depending upon the particularapplication.

In another aspect of the present description, the voice coil actuator320 is sufficiently small to be self-contained within the body of theroller bearing 60 itself, including its base 302. Moreover, the rollerbearing 60, including the base 302, has a form factor for readyimplementation into various tape products. It is appreciated that inother applications, the size and position of the actuator, and the formfactor of the roller bearing, may vary, depending upon the particularapplication.

FIG. 7 depicts one example of operations, in accordance with oneembodiment of the present description, to constrain lateral movement ofa tape. In one operation, a taper roller barrel such as the rollerbarrel 310 of the roller bearing 60, is rotated (block 700) by engaginga surface 200 of the tape roller barrel 310 with a longitudinally movingmagnetic tape, such as the tape 11. In another operation, at least aportion of any air bearing between the moving tape and the barrelsurface is quenched (block 710) using grooves such as the grooves 312,formed in the barrel surface 200.

In accordance with one aspect of the present description, it isrecognized that a tilting grooved roller bearing, such as the rollerbearing 60, which quenches the air bearing between the tape 11 and theroller bearing 60, does not, in this embodiment, operate in the same wayas a tilting smooth roller which could permit an air bearing to bemaintained between the tape 11 and the surface of the roller barrel.Because the air bearing is substantially quenched in the presentembodiment, little or no tension gradient is developed across the tape.Nonetheless, tape 11 is constrained to move in the same direction as thetilting motion of the barrel of the grooved roller.

Accordingly, in additional operations, the lateral position of themoving tape 11 is sensed (block 720) by a sensor such as the sensor 324,and the rotating roller barrel is tilted (block 730) using an actuatorsuch as the actuator 320, in response to the sensed lateral position ofthe moving tape, to control the lateral position of the moving tape.Thus, for example, if the sensor 324 senses the lateral positiondeviating from the center position, the actuator 320 tilts the rollerbarrel 310 which moves the tape back toward the center position. In thismanner, deviation from the center lateral position of the tape relativeto barrel center position may be readily corrected. It is believed thata tilting grooved roller bearing constraint as described herein hassufficient dynamics for closed loop operation. FIGS. 8 a and 8 b depictone example of the dynamics of operation which it is believed may beobtained. FIG. 8 a plots tilt magnitude versus frequency and FIG. 8 bplots phase (in degrees) versus frequency, of the dynamic operations ofa prototype. It is appreciated that other dynamic responses may beobtained, depending upon the particular application.

In one feature of a method of tape steering or guiding in accordancewith the present description, it is believed that there is little or notransition in control on startup. By comparison, such transitions incontrol may be present for a tilting smooth roller, such as duringstartup or shutdown. As a consequence, it is believed that, in a tapemovement constraint in accordance with the present description,effective control can be maintained at all or substantially all times toreduce or eliminate tape damage.

In another feature of a method of tape steering or guiding in accordancewith the present description, it is believed that relatively littlerelative motion occurs between the tape and the grooved surface of theroller bearing, except that lateral motion intentionally caused bytilting the roller bearing. As a consequence, it is believed that highfrequency lateral motion excitations may be controlled. In theillustrated embodiment, the cylindrical peripheral surface 200 comprisesa grooved frictional surface for contacting and engaging the surface ofthe tape and constraining movement of the tape in the lateral direction,while not increasing friction in the longitudinal direction, therebyreducing the rate of the lateral transient movement of the tape to allowthe track following servo system to follow the reduced rate lateraltransient movement of the longitudinal tracks.

Thus, the tape is contacted and engaged at its surface rather than at anedge, limiting lateral slip and providing substantial lateral drag tothe tape, while the tape rolls freely with the tape roller bearing asthe tape roller bearing rotates, substantially altering the transientcharacteristics of the tape and reducing the rate of the lateraltransient movement. Thus, undesirable forces and stresses on the tapeare reduced or prevented. At the same time, as the result of thesubstantial lateral drag provided by the lateral constraint of thegrooved frictional cylindrical peripheral surface 200, the rate oflateral movement is reduced. To move at a high lateral velocity, thetape would need to overcome the frictional contact of the cylindricalperipheral surface 200. This constraint thereby substantially reducesthe lateral velocity of the tape from that which would occur if the tapewere free to slide over the bearing surface.

In yet another feature of a method of tape steering or guiding inaccordance with the present description, it is believed that such methodand apparatus may be readily used with a high wrap angle. By comparison,in the case of a smooth roller bearing, it is believed that a high wrapangle would tend to decrease the height of the self-acting air bearing,and thereby inhibit proper control operation of the smooth bearing.

In the embodiment of FIGS. 2-4, the cylindrical peripheral surface 200of the barrel 310 is grooved with grooves 312 over the full height L ofthe barrel 310. FIGS. 9 a and 9 b show alternative embodiments of thebearing 60 a, 60 b in which the cylindrical peripheral surface 200 isungrooved at each side of the grooves 312 at each edge of the tape toform smooth cylindrical surfaces 910 and 920 to fully support the tapeat the edges. In the embodiment of FIG. 9 b, the bearing 60 b mayfurther have flanges 924, 926 at the ends of the cylindrical surface 200to further constrain lateral movement of the tape. The flanges 924, 926are, thus, optional and may be provided to inhibit the tape from movingoff the tape roller bearing when the tape tension is reduced or toreduce or eliminate excessive lateral movement of the tape due to axialmisalignment of the tape roller bearing.

In some applications, the smooth support provided by smooth surfaces910, 920 may tend to prevent distortion of the tape at the edges and tofurther prevent damage to the tape. Also, excessive amplitude lateralmovement might be further inhibited by conventional tape guiding atadjacent locations.

In the embodiments of FIGS. 2-4 and 9 a, 9 b, the grooved portion of thetape roller bearing frictional cylindrical peripheral surface 200comprises a plurality of lands 930 separated by grooves 312. The lands930 extend about the cylindrical peripheral surface 200 in acircumferential direction generally parallel to the longitudinaldirection that the tape is moved. Any potential air bearing that couldform between the surface of the tape and the surface of the rollerbearing, e.g., due to the air drawn along by the tape as it is movedrapidly, is collapsed to provide contact between the tape surface andthe lands 930 for engaging the surface of the tape. In this example, thelands 930 and grooves 312 extend in the circumferential direction at anacute angle to the longitudinal direction, thereby forming a helicalpattern. As an example, the lands may be as little as 30% of thecombined width of a groove and land. The helical pattern of thefrictional cylindrical peripheral surface extends laterally a lengthless than the width of a tape, to reduce or prevent generation of atrench into the surface of the tape by any one land, e.g., if the landswere non-helical. In order to reduce wear of the tape, the cylindricalperipheral surface lands 930 may be radiused 940 at the grooves 312. Asan example, for lands of 0.10 mm, the radius may be less than 0.02 mm.

FIG. 10 illustrates an alternative embodiment of a grooved rollerbearing 60 c in accordance with the present description, wherein thegrooves 1010 and lands 1020 are substantially parallel to thelongitudinal direction of the tape motion and a smooth cylindricalsurface 1030 is provided at each edge of the bearing to support the tapeedges.

FIG. 11 illustrates a further alternative embodiment of a grooved rollerbearing 60 d. The roller bearing comprises a base material 1105, such asaluminum, coated with an elastomeric coating 1106 for engaging the tape.The coated roller bearing may appear the same as the helically groovedbearings of FIGS. 2-4, 9 a, and 9 b, or as the longitudinally groovedbearing of FIG. 10. The elastomeric coating may have a high coefficientof friction. However, in many embodiments, the coating 1106 wouldtypically not be “sticky” or cling to the tape, to allow the tape tomove more freely in the longitudinal direction.

FIG. 12 illustrates two alternative embodiments of a roller bearing 60 ein accordance with the present description. In a grooved peripheralsurface, such as a machined set of grooves, the grooves 1208 extend in adouble helix crossing pattern, such that the lands 1209 form islands forengaging the surface of the tape. In a textured surface of anelastomeric material, which may be molded, the textured surface maycomprises a negative crosshatch “waffle” pattern of protruding islands1209 above recessed grooves 1208, the protruding islands for contactingand engaging the surface of the tape, and the recessed grooves allowingentrapped air to bleed from between the tape and the cylindricalperipheral surface to collapse any air bearing thereat. A smoothcylindrical surface 1207 is provided at each edge of the bearing tofully support the tape edges.

FIG. 13 illustrates a still further alternative embodiment of a rollerbearing 60 f, wherein the tape roller bearing frictional cylindricalperipheral surface 1310 comprises a roughened surface having protrusionsfor contacting and engaging the surface of the tape, and having groovesin the shape of amorphous, irregular voids allowing entrapped air tobleed from between the tape and the cylindrical peripheral surface tocollapse any air bearing thereat. The roughened surface 1310 may begenerated by sandblasting or by molding, for example. The surface 1310is sufficiently supportive that a smooth surface at the tape edges maybe omitted, thereby facilitating bleeding of air at the tape edges.

Referring to FIGS. 14 a and 14 b, the grooves 312 of the tape rollerbearing may comprise any suitable angle 1410 with respect to the lands930, and any suitable depth, that will assure that entrapped air is bledfrom between the tape and the cylindrical peripheral surface so as tocollapse any air bearing. It has been found that appropriate anglescomprise any angle in a range of substantially 45 degrees, as shown inFIG. 14 a, to substantially 90 degrees, as shown in FIG. 14 b. The taperoller bearing may be made, for example, from a metal, such as aluminumwhich is machined to form the respective lands and grooves. The radii940 of the cylindrical peripheral surface lands 930 at the grooves 312are also illustrated. Alternatively, the tape roller bearing 70 maycomprise a molded plastic or resin.

Those of skill in the art will understand that various materials andtechniques may be employed to provide the roller bearing tape movementconstraint of the present description. Those of skill in the artunderstand that still further alternative peripheral surfaces andtechniques for manufacturing the tilting roller bearing may beenvisioned.

While embodiments of the present description have been illustrated indetail, it should be apparent that modifications and adaptations tothose embodiments may occur to one skilled in the art without departingfrom the scope of the present description as set forth in the followingclaims.

What is claimed is:
 1. A tape movement constraint for a tape drivesystem for a tape, comprising: a base having a first support frame; asecond support frame; a tape roller barrel rotatably supported by saidsecond support frame, said roller barrel being positioned along a tapepath, and having a grooved surface adapted to contact and engage asurface of the tape as said roller barrel rotates; a pivot disposed atthe tape roller barrel and pivotally coupling said second support frameto said first support frame; and an actuator coupled to said secondsupport frame and adapted to pivot said second support frame and saidroller barrel relative to said first support frame when said actuator isactuated.
 2. The constraint of claim 1 wherein said tape drive system isadapted to move said tape along said tape path in a longitudinaldirection across a tape head, said tape having tracks extending in saidlongitudinal direction, said tape head having a track following servosystem for moving said head in a lateral direction with respect to saidlongitudinal direction for following lateral movement of saidlongitudinal tracks as said tape is moved in said longitudinaldirection, said tape subject to transient movement in a lateraldirection with respect to said longitudinal direction, said constraintfurther comprising: a tape position sensor positioned to detect thelateral position of the tape; and a controller responsive to the tapeposition sensor and adapted to control the actuator to tilt the rollerbarrel to control the lateral position of the tape in response to thetape position sensor.
 3. The constraint of claim 2 wherein said actuatorincludes a coil adapted to conduct an electric current to generate amagnetic field, said second support frame including a coil holderadapted to hold said coil.
 4. The constraint of claim 3 furthercomprising a bearing track positioned around and supported by said coilholder and engaging said roller barrel, wherein said roller barrel isadapted to rotate on said bearing track around said coil holder of saidsecond support frame.
 5. The constraint of claim 4 wherein said pivotcomprises a hinge disposed in said coil holder wherein said coil holderis pivotally coupled to said first support frame by said hinge.
 6. Theconstraint of claim 5 wherein said roller barrel surface has a centerposition in said lateral direction and said hinge defines a pivot axisaligned with said center position.
 7. The constraint of claim 5 whereinsaid hinge is a living hinge which includes first and second hingemembers and a flexure member flexibly coupling said first hinge memberto said second hinge member, said first hinge member being coupled tosaid coil holder and said second hinge member being coupled to saidfirst support frame.
 8. The constraint of claim 3 wherein said actuatorfurther comprises at least one permanent magnet disposed in said baseand having a magnetic field positioned to interact with the magneticfield generated by the coil to cause the coil to move with respect tothe magnet.
 9. A tape drive system for a tape having tracks extending ina longitudinal direction along the tape, comprising: a tape head; adrive adapted to move said tape along a tape path in a longitudinaldirection across said tape head; a tape position sensor positioned todetect the lateral position of the tape; a tape roller bearing,comprising: a base having a first support frame; a second support frame;a tape roller barrel rotatably supported by said second support frame,said roller barrel being positioned along a tape path, and having agrooved surface adapted to contact and engage a surface of the tape assaid roller barrel rotates; a pivot disposed at the tape roller barreland pivotally coupling said second support frame to said first supportframe; and an actuator coupled to said second support frame and adaptedto pivot said second support frame and said roller barrel to tilt saidroller barrel relative to said first support frame when said actuator isactuated; and a controller responsive to the tape position sensor andadapted to control the actuator to tilt the roller barrel to control thelateral position of the tape in response to the tape position sensor.10. The system of claim 9 wherein said actuator includes a coil adaptedto conduct an electric current to generate a magnetic field, said secondsupport frame including a coil holder adapted to hold said coil.
 11. Thesystem of claim 10 further comprising a bearing track positioned aroundand supported by said coil holder and engaging said roller barrel,wherein said roller barrel is adapted to rotate on said bearing trackaround said coil holder of said second support frame.
 12. The system ofclaim 11 wherein said pivot comprises a hinge disposed in said coilholder wherein said coil holder is pivotally coupled to said firstsupport frame by said hinge.
 13. The system of claim 12 wherein saidroller barrel surface has a center position in said lateral directionand said hinge defines a pivot axis aligned with said center position.14. The system of claim 12 wherein said hinge is a living hinge whichincludes first and second hinge members and a flexure member flexiblycoupling said first hinge member to said second hinge member, said firsthinge member being coupled to said coil holder and said second hingemember being coupled to said first support frame.
 15. The system ofclaim 10 wherein said actuator further comprises at least one permanentmagnet disposed in said base and having a magnetic field positioned tointeract with the magnetic field generated by the coil to cause the coilto move with respect to the magnet.